Method and arrangement in a telecommunication system

ABSTRACT

There is provided a method for use in a user equipment when the user equipment is in idle mode or any other low activity state, and when the user equipment bandwidth is smaller than the cell transmission bandwidth. The method comprises the steps of determining a paging position of the user equipment in the frequency domain; receiving, from the network, paging information within the user equipment reception bandwidth; and changing, if indicated by the network, the paging position of the user equipment within the cell transmission bandwidth.

RELATED APPLICATIONS

This application claims priority and benefit from InternationalApplication No. PCT/EP2007/007392, filed Aug. 22, 2007, which claimspriority to Swedish Patent Application No. 0601716.4, filed Aug. 22,2006, the entire teachings of which are incorporated herein byreference.

The present invention relates to methods and arrangements in atelecommunication system, in particular to methods and arrangements forpaging transmissions in variable bandwidth scenarios.

BACKGROUND

In current systems such as, e.g., the UMTS Terrestrial Radio AccessNetwork (UTRAN) the reception bandwidth of user equipments (UEs) is thesame as the cell transmission bandwidth. However, in Evolved UTRAN(E-UTRAN) the system may employ variable bandwidths. Further, theminimum bandwidth that is applied by a user equipment can be smallerthan the network bandwidth. For instance, a typical case in futurereleases of E-UTRAN would be a 20 MHz user equipment operating in asystem comprising a 30 MHz or 40 MHz cell transmission bandwidth. Oneadditional important aspect of E-UTRAN is the potentially very largenumber of active and idle mode users per cell. This is partly due to thepossibly large bandwidth that can be applied (10 MHz and 20 MHz cases)and partly because of the packet-oriented design. Hence, the number ofpaging messages per cell is envisioned to be much larger compared toprevious radio access networks, e.g. the UTRAN or GERAN system, and, asa consequence, paging in E-UTRAN may consume more resources than inother systems.

In E-UTRAN, no radio resources are allocated to a user equipment in idlemode and, thus, there is no RRC connection maintained (see, e.g., thedocuments 3GPP TS25.304, “UE procedures in idle mode and procedures forcell reselection in connected mode” and 3GPP TS25.331, “Radio ResourceControl Protocol Specifications” issued by the 3rd GenerationPartnership Project). Therefore, the user equipment is informed about anincoming call by help of a paging indication. In case of an incomingcall the network can page the user equipment, whereby the informationrelates to the call only at a well defined instance, i.e. once per DRXcycle. This implies that user equipments need to monitor the pagingindication once per DRX cycle. As E-UTRAN fully employs packet switchingtechnology, it requires efficient paging mechanisms since the packetarrival (i.e. incoming calls) is bursty.

According to current solutions the paging is sent in the centre of thetransmission bandwidth. This solution works well for user equipmentshaving a bandwidth that is the same as the cell transmission bandwidth.However, in some E-UTRAN scenarios the bandwidth of the user equipmentis smaller than the network bandwidth. For such scenarios a userequipment must retune its receiver each time it needs to listen to thepaging. Further, current solutions also lead to less flexibility interms of resource allocation from the network perspective.

SUMMARY OF INVENTION

It is thus perceived to be a problem to achieve a dynamic allocation ofresources for paging that is applicable also in scenarios where thebandwidth of a user equipment is smaller than the network bandwidth andwhere the user equipment only can use limited positions in the frequencydomain.

It is therefore the basic idea of the present invention to achieve amethod and arrangement in a user equipment operating with a bandwidththat is smaller than its cell transmission bandwidth, said methodincluding the steps of indicating its paging position in the frequencydomain to the network; receiving paging information, or an appropriatemessage within the UE reception bandwidth, from the network; changing,if indicated by the network, its paging position within the celltransmission bandwidth. The method may further include the steps ofreceiving and applying selection probabilities for different possiblepaging positions within the cell transmission bandwidth that arebroadcasted by the network in order to ensure for a cell an evendistribution of user equipments in the frequency domain.

According to a second aspect of the present invention, there is alsoprovided a method in a network unit, the method comprising the step ofpositioning a user equipment at a particular position in the frequencydomain for receiving paging when the user equipment is in idle mode orany other low activity state.

According to third and fourth aspects of the present invention, a userequipment and a network unit are provided for performing the methods ofthe first and second aspects, respectively, as outlined above.

The present invention implies the advantage to ensure an equaldistribution in the frequency domain of paging positions of userequipments within the cell transmission bandwidth.

It is a further advantage of the present invention that it ensures anefficient usage of resources by preventing the need of sending multiplecopies of paging indications and paging messages.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show moreclearly how it may be carried into effect, reference will now be made,by way of example, to the following drawings, in which:

FIG. 1 shows a cellular radio communication network;

FIG. 2 illustrates an example of locations in the frequency domain of a20 MHz UE in a 40 MHz cell transmission bandwidth;

FIG. 3 shows an example of paging of a 20 MHz UE in a 40 MHz celltransmission bandwidth; and

FIG. 4 illustrates the signalling for indicating and negotiating UEpositions within the cell bandwidth.

DETAILED DESCRIPTION

FIG. 1 shows a cellular radio communication network 10. The network 10comprises a plurality of network units 20, each of which transmitscommunications to a separate cell in the network 10. Network units 20are also referred to as base stations in the following description.Within each cell, user equipments (UEs) 30 receive transmissions fromthe respective network unit 20. Each of the network units 20 receiveinformation from a core network (CN) 40, which controls the operation ofthe network 10.

The present invention relates to the scheduling of paging indicationsand paging messages to user equipments having a bandwidth that issmaller than the cell transmission bandwidth. The user equipment shallbe positioned in the frequency domain at limited positions. By means ofa non-limiting example, which is applied in the following description,in E-UTRAN the minimum UE bandwidth capability is 20 MHz and the maximumcell bandwidth in future will be larger than 20 MHz. Hence, as anexample, in E-UTRAN a 20 MHz user equipment within a 40 MHz cellbandwidth shall be placed at a limited number of positions (e.g. two orthree positions). For this purpose the user equipment tunes its receiverto a specific position in the frequency domain within a cell. FIG. 2shows an example of 20 MHz UE with two different positions in thefrequency domain: lower (left) 20 MHz or upper 20 MHz (right).

Regarding paging transmission, both the paging indicator and the pagingmessage are sent within the UE reception bandwidth without anyduplication (the paging can be sent at any position in the frequencydomain within the UE reception bandwidth). Since the user equipment ispaged within its reception bandwidth it is prevented that the userequipment needs to re-tune its receiver. FIG. 3 shows the transmissionof paging in case of two UE positions.

Alternatively, if the paging is duplicated, or multiple pagings are sentin case of more than two UE positions, the user equipment would beallowed to receive the paging irrespective of its position and withoutthe need for any re-tuning of its receiver. In order to allow the abovesolution to work the network needs to be aware of the current pagingposition of the user equipment within the cell transmission bandwidth,which is larger than the UE bandwidth. In a first step the userequipment needs to be positioned at a certain paging position.

The following discloses by means of non-limiting examples severalembodiments to position a user equipment:

According to one embodiment for positioning of a user equipment in thefrequency domain, a certain positioning rule is applied, e.g. aprobabilistic or a hash-based rule.

1) When applying, for instance, a probabilistic rule, the user equipmentselects its paging position out of a number N of possible positions witha certain probability that is associated to each position. Thus, aposition that is denoted with a positioning index kε[0, 1, . . . N−1] isselected by the user equipment with a probability P_(k). In a specialcase the probabilities for all positions are the same, i.e. P₀=P₁= . . .P_(N-1)=1/N. In case of two UE positions, the above special case wouldimply that statistically half of the user equipments are positioned onthe lower half of the spectrum and half of the user equipments arepositioned on the upper half of the spectrum.

2) Another conceivable positioning rule is a hash rule that is based ona suitable hash function. In this rule user equipments are positioned inthe frequency domain according to their identities (ID). Hashing of theUE identifier maps then the UE identity on one of the availablepositions. One simple example of hashing function is a modulusoperation, whereby a user equipment is positioned in the frequencydomain according to a UE-specific identifier (UE_ID). For instance, outof a number N of possible positions the user equipment can derive itspositioning index k by using an operation k=(UE_ID) mod N. A UE-specificidentifier is, e.g., the IMSI; however, any other well-definedUE-specific identity can be used.

In another hash-based rule, the groups of UE identities can be mappedonto paging positions. UE identities can be hashed onto paging groups(e.g. 32-bit UE_ID to 12 bit Paging Group ID) which are, in turn,deterministically distributed over the available paging positions.

According to another embodiment for positioning a user equipment in thefrequency domain, the UE positioning can be performed either by aUE-based selection, i.e. the user equipment places itself independentlyat a certain position, or by a network-based selection. As the pagingconsumes a certain amount of resources it is beneficial to equallydistribute the idle mode user equipments, i.e. those listening to thepaging, within the different positions in the frequency domain. Thenetwork is fully aware of the radio resource situation and can thereforeindicate in the system information (transmitted on the broadcastchannel) the preferred paging positions where the user equipment shalltune itself. Depending on the type of information that is sent in thesystem information there are different possible ways to realize thismechanism, whereof the following discloses two non-limiting examples:

1) Well Defined Positions: The broadcasted information may compriseassociations between the range of UE identities, or groups of UEidentities, and the paging positions. The UE groups that are to beassigned to different paging positions can be decided on by help oftheir identities, subscription, intended services, or any other suitablecriteria.

2) Broadcast Selection Probabilities: The system information maycomprise selection probabilities for different paging positions. Theprobabilities could be changed dynamically owing to the radio resourceusage in different locations. This method provides an increasedflexibility. For instance, if needed, a non-uniform UE distribution canalso be achieved by changing the access probabilities. This means that auser equipment shall automatically be placed at the paging position thatis optimal from a resource usage view point. Thus, this allowspreventing a resource bottleneck at the time of paging.

After having retrieved a paging position for the user equipment in thefrequency band, it is necessary to report the paging positions. The userequipment (in idle mode) selects a suitable paging position, e.g. byusing any of the methods described above. Subsequently, the userequipment then reports, depending on the used position selection method,its paging position to the network (except for hash based rules). Thisis necessary because the network needs to know the frequency position atwhich the user equipment currently is camped before the network can sendthe page. The user equipment can indicate its paging position, e.g., ina location management message (e.g. tracking area update, cell updateetc). The message may simply consist of an identity of the pagingposition, e.g. by applying an M-bit message to report 2^(M) positions.However, it must be observed that the user equipment can move within thecoverage area and, thus, may camp on to a new cell. Preferably, the userequipment shall maintain the same paging position at least in the sametracking area. However, in case the paging position of the userequipment within the cell bandwidth is different in the new cellcompared to the old cell, the user equipment shall again indicate itsnew paging position the network. In response, the network shall send apaging indicator as well as a paging message to the new paging positionin the frequency domain at which the user equipment is tuned. This meansthat user equipments in a particular paging position may be assigned thesame group identity in case this group identity is used to addresspaging related information. The network also has the liberty to directthe user equipment to change its paging position. This could be done bysending the request to the user equipment in a location managementmessage, e.g. tracking area update confirm, cell update confirm etc. Theentire protocol operation is shown in FIG. 4. In said figure, the userequipment in idle mode or any low activity state receives a broadcastmessage 31 from the Node B with UE position-related information. Theuser equipment selects 32 its paging position within the celltransmission bandwidth and reports the paging position-ID in, e.g., alocation management message 33. The network assigns 34 paging group IDand may request the user equipment to retune its paging position in alocation management message 35.

The main benefit of the pre-defined rules is that the Core Network, e.g.the access gateway in E-UTRAN, does not need to inform the base stationwhere to page the user equipment. It is already sufficient to inform thebase station about the identity of the user equipment. If the basestation has been supplied with the particular “rule”, the base stationcan calculate itself at which paging position in the frequency domainthe user equipment is camped. The base station will then send the pagingfor that particular user equipment at that particular paging position.

The applied “rule” should preferably not be hard-coded into the userequipment but rather be provided at the time when the user equipmentattaches to the network. This allows to use the benefits of the usage ofa network-controlled rule, e.g. to simplify an update of a hashfunction, which has turned out to have some bad properties. Secondly asstated earlier, this also provides a more flexible and efficienthandling of the radio resources.

Although the above examples have mainly concentrated on a 40 MHz celltransmission bandwidth and a 20 MHz UE bandwidth, it will be appreciatedby those skilled in the art that the present invention is equallyapplicable to any range of bandwidths and frequencies, as long as the UEbandwidth is smaller than the cell transmission bandwidth. One exampleis that of a 20 MHz bandwidth UE operating in a cell with 30 MHzbandwidth.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. The word “comprising” does not excludethe presence of elements or steps other than those listed in a claim,“a” or “an” does not exclude a plurality, and a single processor orother unit may fulfil the functions of several units recited in theclaims. Any reference signs in the claims shall not be construed so asto limit their scope.

The invention claimed is:
 1. A method for a user equipment unit in acellular radio communication network, said method comprising: selectinga paging position within a network bandwidth, wherein the user equipmentreceives paging indications from the network according to the pagingposition, the user equipment is operating using a reception bandwidththat is smaller than the network bandwidth, and the user equipment ismonitoring for the paging indication while operating in at least one ofidle mode or another low activity state; and changing the pagingposition to a second paging position based on an explicit indicationsent by the network, the explicit indication being sent using adedicated signaling message sent to the user equipment from the network.2. The method according to claim 1, wherein the user equipment selectsthe paging position using one or more predefined rules.
 3. The methodaccording to claim 2, wherein the user equipment selects the pagingposition according to a rule related to predefined probabilities foreach position.
 4. The method according to claim 2, wherein the userequipment selects the paging position according to a rule related to ahash function.
 5. The method according to claim 4, wherein the changingincludes hashing an identity of the user equipment onto another pagingposition that is different from the selected paging position and that isavailable according to the hash function.
 6. The method according toclaim 4, wherein identities of plural user equipments including the userequipment are hashed onto a paging group and are assigned to differentpaging positions.
 7. The method according to claim 1, wherein the userequipment selects the paging position according to received broadcastinformation.
 8. The method according to claim 1, wherein the dedicatedsignaling message comprises one or more of a tracking area updateconfirm message or a cell update confirm message.
 9. The methodaccording to claim 1, wherein the user equipment selects the pagingposition according well-defined positions that are associations betweenuser equipment identities and paging positions.
 10. The method accordingto claim 1, further comprising reporting the selected paging position tothe network during a location management after an initial cellselection.
 11. The method according to claim 1, further comprisingreporting the selected paging position to the network during a locationmanagement after a cell re-selection.
 12. The method according to claim1, further comprising: receiving the paging indication labeled accordingto an identity of the user equipment, from the network according to thepaging position; and changing a state of the user equipment from theidle mode or the low activity state in response to the receiving.
 13. Amethod for paging transmission, for use in a network unit of a cellularradio communication network comprising one or several user equipmentsoperating with a bandwidth that is smaller than the network bandwidth,said method comprising: transmitting, to a user equipment, a pagingindication according to a paging position selected by the user equipmentthat is within the network bandwidth, the paging indication being sentwhile the user equipment is in idle mode or another low activity state;and transmitting, to the user equipment, a dedicated signaling messagethat explicitly indicates a change to a second paging position to beused by the user equipment for subsequent paging indications.
 14. Themethod of claim 13, further comprising: receiving the paging positionfrom the user equipment.
 15. The method of claim 13, further comprising:transmitting a paging message to the user equipment within the samereception bandwidth used for transmitting the paging indication.
 16. Themethod according to claim 13, further comprising broadcasting selectionprobabilities to achieve a random distribution of the user equipmentsamong different possible paging positions.
 17. The method according toclaim 13, further comprising: periodically requesting the user equipmentto retune the paging position.
 18. A user equipment for use in acellular radio communication network, the user equipment beingconfigured to: select a paging position within the network bandwidth,wherein the user equipment is configured to receive a paging indicationfrom the network according to the paging position, the user equipment isconfigured to operate using a reception bandwidth that is smaller thanthe network bandwidth, and the user equipment is configured to monitorfor the paging indication while operating in at least one of idle modeor another low activity state; and change the paging position of theuser equipment to a second paging position based on an explicitindication sent by the network, the explicit indication being sent usinga dedicated signaling message sent to the user equipment from thenetwork.
 19. A network unit, for use in a cellular radio communicationnetwork comprising one or more user equipments operating with abandwidth that is smaller than a network bandwidth, said network unitbeing configured to: transmit a paging indication to a user equipment ata paging position selected by the user equipment that is within thenetwork bandwidth, the paging indication being sent while the userequipment is in idle mode or another low activity state; and transmit,to the user equipment, a dedicated signaling message that explicitlyindicates a change to a second paging position to be used by the userequipment for subsequent paging indications.